Make metrics pretty_print.py scripts runnable from git cl format.

tools/metrics/common/presubmit_util.py

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import difflib
+import logging
 import os
+import shutil
 import sys
-import logging
-import shutil
 
 sys.path.append(
     os.path.join(os.path.dirname(os.path.abspath(__file__)),
                  os.pardir, os.pardir, 'python', 'google'))
 import path_utils
 
 import diff_util
 
 def DoPresubmitMain(argv, original_filename, backup_filename, script_name,
                     prettyFn):
   """Execute presubmit/pretty printing for the target file.
 
   Args:
     argv: command line arguments
     original_filename: The filename to read from.
     backup_filename: When pretty printing, move the old file contents here.
     script_name: The name of the script to run for pretty printing.
     prettyFn: A function which takes the original xml content and produces
         pretty printed xml.
 
   Returns:
     An exit status.  Non-zero indicates errors.
   """
-  logging.basicConfig(level=logging.INFO)
+  # interactive: Print log info messages and prompt user to accept the diff.
+  interactive = ('--non-interactive' not in argv)
+  # presubmit: Simply print a message if the input is not formatted correctly.
   presubmit = ('--presubmit' in argv)
+  # diff: Print diff to stdout rather than modifying files.
+  diff = ('--diff' in argv)
+
+  if interactive:
+    logging.basicConfig(level=logging.INFO)
+  else:
+    logging.basicConfig(level=logging.ERROR)
 
   # If there is a description xml in the current working directory, use that.
   # Otherwise, use the one residing in the same directory as this script.
   xml_dir = os.getcwd()
   if not os.path.isfile(os.path.join(xml_dir, original_filename)):
     xml_dir = path_utils.ScriptDir()
 
   xml_path = os.path.join(xml_dir, original_filename)
 
   # Save the original file content.
   logging.info('Loading %s...', os.path.relpath(xml_path))
   with open(xml_path, 'rb') as f:
     original_xml = f.read()
 
   # Check there are no CR ('\r') characters in the file.
   if '\r' in original_xml:
     logging.error('DOS-style line endings (CR characters) detected - these are '
                   'not allowed. Please run dos2unix %s', original_filename)
     sys.exit(1)
 
   try:
     pretty = prettyFn(original_xml)
   except Exception as e:
     logging.exception('Aborting parsing due to fatal errors:')
     sys.exit(1)
 
   if original_xml == pretty:
     logging.info('%s is correctly pretty-printed.', original_filename)
     sys.exit(0)
+
   if presubmit:
     logging.error('%s is not formatted correctly; run %s to fix.',
                   original_filename, script_name)
     sys.exit(1)
 
   # Prompt user to consent on the change.
-  if not diff_util.PromptUserToAcceptDiff(
+  if interactive and not diff_util.PromptUserToAcceptDiff(
       original_xml, pretty, 'Is the new version acceptable?'):
     logging.error('Diff not accepted. Aborting.')
     sys.exit(1)
 
+  if diff:
+    for line in difflib.unified_diff(original_xml.splitlines(),
+                                     pretty.splitlines()):
+      print line
+    sys.exit(0)
+
   logging.info('Creating backup file: %s', backup_filename)
   shutil.move(xml_path, os.path.join(xml_dir, backup_filename))
 
   with open(xml_path, 'wb') as f:
     f.write(pretty)
   logging.info('Updated %s. Don\'t forget to add it to your changelist',
                xml_path)
   sys.exit(0)